Currently, flexographic printing plates for printing machines are generally mounted on the printing plate cylinder by aligning as precisely as possible reference points (for example the traditional registration marks) provided on the printing plates with respective reference markings (often still marked by hand) on the sheets of paper on which the test prints are to be performed.
Modern machines avoid having to perform this alignment of reference markings every time with the naked eye, since optical magnification means are provided or, in the most advanced versions, television cameras are provided which allow to view under magnification the chosen points to be aligned.
Once the fixing of a first printing plate related to one color has been performed correctly and once the test print with said first printing plate has been performed, by way of said optical control means it is possible to verify and optimize the fixing of the printing plates related to the other colors to the respective printing plate cylinders.
It is evident that it is necessary to perform practical overlapping test prints of the image for each cylinder in order to check the achieved result of the in-register mounting of the printing plate; this of course requires considerable time for programming the positions of the printing plates and performing the test prints to check the perfect positioning of each printing plate, and such time is currently no longer acceptable, since it does not allow to achieve the optimum production rates required by the market.
Plate mounting devices, known simply as pointers, have become commercially widespread and allow, after programming the coordinates that correspond to the position of the mounting references, to position automatically the television cameras above the printing plate cylinder. The use of pointers, therefore, requires considerable time for programming, and it is possible only to check the mounting position of the references (for example, the traditional registration marks or microdots).